1. Field of The Invention
The present invention relates to a control apparatus for an inverter which feeds an induction motor on the basis of a vector control, especially to an inverter control apparatus, in which various control constants necessary for the processing operation of the vector control can be adjusted by itself in response to constants of the induction motor fed by the inverter.
2. Description of The Related Art
Nowadays, an inverter-fed induction motor is often controlled on the basis of a so called vector control, in which a primary current of the induction motor is resolved into a torque current component and a magnetizing current component which are separately controlled independent of each other, so that the high performance speed control of the induction motor can be attained. In such vector control, various control constants to be set in an inverter control apparatus must be determined in response to constants of an induction motor fed from the inverter.
In vector oontrol apparatus disclosed in Japanese Patent Laid-open Publication Nos. 59-165982 (published on Sept. 19, 1984) and 61-52176 (published on Mar. 3, 1986), for example, motor constants, such as primary resistance, primary inductance, leakage inductance and secondary resistance, are utilized as control constants in those control apparatus in order to calculate reference signals for controlling the output voltage of an inverter.
Conventionally, the control constants are manually set in the control apparatus on the basis of designed values of the motor constants. Therefore, troublesome works are necessitated, because the control constants in a control apparatus must be changed whenever an induction motor associated with the control apparatus is replaced. Further, the disagreement between the designed values and actual ones of the motor constants results in error occuring in course of calculation of voltage reference signals, which causes the torque produced by the induction motor to fluctuate.
To resolve the aforesaid problems, there is provided a control apparatus as disclosed in Japanese Patent Laid-open Publication No. 61-92185. According to this apparatus, an induction motor is fed by an inverter which operates in accordance with a predetermined reference signal for a motor current, and a motor voltage, i.e., an output voltage of the inverter, is detected various motor constants are identified from the relation between the predetermined motor current reference and the detected motor voltage, and the control constants in the control apparatus are set in accordance with the identified motor constants.
In the prior art mentioned above, however, there must be provided a particular voltage detector, which is exclusively used only for obtaining the motor constants. Further, since the voltage detected by the voltage detector usually has a distorted waveform, it is detected with a low accuracy, with result that the accuracy of the determination of the control constants also becomes low.